[GitHub] [geode] Bill commented on a change in pull request #5666: GEODE-8652: Allow NioSslEngine.close() to Bypass Locks

[GitBox <gi...@apache.org>]

Bill commented on a change in pull request #5666:
URL: https://github.com/apache/geode/pull/5666#discussion_r512933947



##########
File path: geode-core/src/main/java/org/apache/geode/internal/net/ByteBufferSharingImpl.java
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@@ -0,0 +1,142 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more contributor license
+ * agreements. See the NOTICE file distributed with this work for additional information regarding
+ * copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License. You may obtain a
+ * copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package org.apache.geode.internal.net;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.apache.geode.annotations.VisibleForTesting;
+import org.apache.geode.internal.net.BufferPool.BufferType;
+
+/**
+ * An {@link AutoCloseable} meant to be acquired in a try-with-resources statement. The resource (a
+ * {@link ByteBuffer}) is available (for reading and modification) in the scope of the
+ * try-with-resources.
+ */
+class ByteBufferSharingImpl implements ByteBufferSharing {
+
+  static class LockAttemptTimedOut extends Exception {
+  }
+
+  private final Lock lock;
+  private final AtomicBoolean isClosed;
+  // mutable because in general our ByteBuffer may need to be resized (grown or compacted)
+  private ByteBuffer buffer;
+  private final BufferType bufferType;
+  private final AtomicInteger counter;
+  private final BufferPool bufferPool;
+
+  /**
+   * This constructor is for use only by the owner of the shared resource (a {@link ByteBuffer}).
+   *
+   * A resource owner must invoke {@link #alias()} once for each reference that escapes (is passed
+   * to an external object or is returned to an external caller.)
+   *
+   * This constructor acquires no lock. The reference count will be 1 after this constructor
+   * completes.
+   */
+  ByteBufferSharingImpl(final ByteBuffer buffer, final BufferType bufferType,
+      final BufferPool bufferPool) {
+    this.buffer = buffer;
+    this.bufferType = bufferType;
+    this.bufferPool = bufferPool;
+    lock = new ReentrantLock();
+    counter = new AtomicInteger(1);
+    isClosed = new AtomicBoolean(false);
+  }
+
+  /**
+   * The destructor. Called by the resource owner to undo the work of the constructor.
+   */
+  void destruct() {
+    if (isClosed.compareAndSet(false, true)) {
+      dropReference();
+    }
+  }
+
+  /**
+   * This method is for use only by the owner of the shared resource. It's used for handing out
+   * references to the shared resource. So it does reference counting and also acquires a lock.
+   *
+   * Resource owners call this method as the last thing before returning a reference to the caller.
+   * That caller binds that reference to a variable in a try-with-resources statement and relies on
+   * the AutoCloseable protocol to invoke close() on the object at the end of the block.
+   */
+  ByteBufferSharing alias() {
+    lock.lock();
+    addReference();
+    return this;
+  }
+
+  /**
+   * This variant throws {@link LockAttemptTimedOut} if it can't acquire the lock in time.
+   */
+  ByteBufferSharing alias(final long time, final TimeUnit unit) throws LockAttemptTimedOut {
+    try {
+      if (!lock.tryLock(time, unit)) {
+        throw new LockAttemptTimedOut();
+      }
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      throw new LockAttemptTimedOut();
+    }
+    addReference();
+    return this;
+  }
+
+  @Override
+  public ByteBuffer getBuffer() throws IOException {
+    if (isClosed.get()) {
+      throw new IOException("NioSslEngine has been closed");
+    } else {
+      return buffer;
+    }
+  }
+
+  @Override
+  public ByteBuffer expandWriteBufferIfNeeded(final int newCapacity) throws IOException {
+    return buffer = bufferPool.expandWriteBufferIfNeeded(bufferType, getBuffer(), newCapacity);
+  }
+
+  @Override
+  public void close() {
+    dropReference();
+    lock.unlock();
+  }
+
+  private int addReference() {
+    return counter.incrementAndGet();
+  }
+
+  private int dropReference() {

Review comment:
       This is a `private` method. We know, in this method, that if `usages == 0` that `destruct()` has been called (in the past), since: the constructor started us with `counter.get() == 1` and `addReference()` is called for every `alias` call.
   
   Because we know `destruct` has been called we know that `isClosed.get()` is already true.




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